A body still remains trapped in the wreckage of a plane that plunged into the sea off Victoria's surf coast five days ago, police believe.

Water Police returned to the crash zone off Barwon Heads, near Geelong, on Tuesday morning with special sonar equipment to find the fuselage of the Piper Cherokee aircraft that crashed on Friday afternoon, killing all four people on board.

It's not known who was flying on Friday, but Mr Hateley - an experienced pilot - sometimes flew Mr Chamberlain's plane, according to those who knew him.

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Inspector Graham Banks of Geelong police said investigators were searching for a male body. He said the coroner's office was working to formally identify the other three victims, as the search continued for their missing flying companion.

"Our main objective is to find the fourth person," he told Fairfax Media on Tuesday morning.